Recent content by robmort

You think Vaillant's MI's are wrong then? I'm saying that clearly at 5kW the min is as given, and at higher power a higher flow rate is needed as given by opening TRV's etc., and of course this is matched by the boiler modulating.

No of course I'm not saying that, but the MI requires 20.3l/min minimum for the 428. When the heat ouput from radiators is less than the minimum heat ouput of the boiler (when TRVs close under warm conditions or only a few radiators are needed) the differential temp across the boiler approaches...

It's necessary to maintain a minimum flow rate through the boiler e.g. to stop kettling which damages it. On the contrary that's exactly what an LLH or CCT do!!

I found this explanation very clear from Chris Watkins on https://www.ukplumbersforums.co.uk/threads/theoretical-questions-regarding-low-loss-headers-or-close-coupled-tees.102592/page-2: "Hydraulic separation using a LLH (expensive) or close coupled tees (cheap) allows modern boilers to...

So not working correctly is normal?? And everything other people have said is down to bad installations???

It's obvious: according to Vaillant the boiler should work under these conditions, but doesn't.

The installers are no use to me, and must have based their system on Vaillant's information which was surely faulty. I find it hard to believe the boiler is supposed to work this way, cutting out so quickly after starting a cycle and not modulating down. Other boliers don't do this.

Despite all the discussion, I can't see any real solutions mentioned. In fact my derating has not worked fully but has helped a bit. There is still a problem with hot water only or with low heating load. My boiler was installed early 2014 and is still under guarantee till 2019, but not sure if...

I've just bought a house with a 428 and with this problem which was very puzzling as it seems the last owner just ignored it and the service technicians also. After much reading here and elsewhere and trying to understand the problem even with a Vaillant qualified gas technician, and trial and...

Of course if you misquote me you can make up anything. I said "several" times. The gap is specified as 3.5mm. You should have seen the electrodes in my boiler; the gap was 8-9mm. This had caused arcing outside the spark plug to the case etc. before the PCB failed.

As in all electronic ignition systems (e.g. for cars), the maximum HT voltage generated is limited by the HT coil and its input voltage from the PCB. The spark jumps the gap of the HT electrodes when the HT voltage reaches a value it needs. At a normal spark gap the spark is created well before...

Well in that case it'd be pretty obvious from the stains etc...... But often there's no obvious reason, so I suggest the above check.

I've had an ISAR HE30 for 9 years without problems and it's still in good condition. The ignition electrodes need to be adjusted occasionally to close the gap as they burn away. Had a few problems at the start due to bad installation, not flushing the existing pipework. Rob

The reason the PCB often fails is that the contacts of the spark ignition are burnt away and too wide apart, causing the PCB to work too hard in generating spark power. So you should always check the spark plug to avoid this happening again. Rob